Not applicable.
(1) Field of the Invention
This invention generally relates to trajectory control and more specifically to a method and apparatus for providing guidance parameters at launch that direct a pursuing vehicle from a launching vehicle to a target vehicle capable of evasive maneuvering when the target vehicle becomes alerted to the presence of the pursuing vehicle at when the pursuing vehicle enables its seeker mechanism.
(2) Description of the Prior Art
The trajectory control of a pursuing vehicle can be classified as post-launch or pre-launch control. In post-launch control, guidance information is sent from the launching vehicle to guide the pursuing vehicle to the target vehicle.
More specifically, in prior art post-launch control systems, a pursuing vehicle exits a launching vehicle. Control systems on the launching vehicle monitor the relative positions of the pursuing vehicle and a target vehicle or contact and control the pursuing vehicle by the transfer of information between the launching vehicle and the pursuing vehicle over a communications link. When the launching vehicle is a submarine and the pursuing vehicle is a torpedo, the communications link typically comprises a communications wire. If the pursuing vehicle is a missile the communications typically occurs over some radio link. In either case, post-launch control systems on the launching vehicle issue guidance parameters to guide the pursuing vehicle along some trajectory into a predetermined relationship with the target vehicle.
In a pre-launch system, the pursuing vehicle follows a predetermined trajectory after launch that may or may not be programmable prior to launch. However, with either type, the pursuing vehicle leaves the launching vehicle and travels along a trajectory that may be simple or complicated. With torpedoes, missiles and the like that may undergo pre-programmed maneuvers, the input guidance parameters may include gyro angles and time lapses or run distances computed from these time lapses, including, for example, the time lapse between the launch and the enablement of any instrumentation on the pursuing vehicle, such as an acoustic seeker on a torpedo.
In order to provide the most accurate pre-launch guidance parameters to the pursuing vehicle, it is necessary that the interval between the time a last estimate of target vehicle state is made and the time a pursuing vehicle is launched be quite short. It is during this interval that a prior art pre-launch system must produce the guidance parameters, and this interval has constrained the nature of the analysis required to produce such guidance parameters. For example, prior art pre-launch systems generally assume that the target will maintain a constant velocity even after the target becomes alerted to the presence of the pursuing vehicle. In actual practice, however, a target normally takes evasive action by turning, changing speed or both. Some prior art pre-launch systems take such actions into account by launching two or more pursuing vehicles along the calculated course and one or more offset courses.
U.S. Pat. No. 5,828,571 (1998) to Bessacini et al. discloses a method and apparatus that overcomes many of the foregoing problems and deficiencies. This method and apparatus provide pre-launch guidance parameters within a short time interval and take evasive action of a target vehicle into account. Models of the pursuing vehicle and target vehicle provide proposed trajectories based upon various environmental considerations and possible evasive tactics. A guidance system uses estimates of initial operating parameter solutions, such as gyro angle, alertment time and intercept time, to begin a convergent, iterative process that defines final operating parameter solutions from which the guidance parameters are determined and transferred to the pursuing vehicle at launch.
In accordance with the method and apparatus disclosed in U.S. Pat. No. 5,828,571 an operator enters an evasive action as an initial parameter that can be independent of the tactical situation facing the target vehicle. That is, the selection of a particular evasive action is somewhat arbitrary or subjective because the selection is primarily dependent on the experience of an operator at the launching vehicle. While the operator may guess the general nature of an evasive action, the operator determines the evasive action without knowledge, for example, of the actual bearing from the target vehicle to the pursuing vehicle at alertment. However, in general, the target vehicle will base an actual evasive action upon that bearing. The evasive actions that the operator guesses and the target vehicle takes may be the same in general terms; for example, a turn of 90xc2x0. However, the actual courses will differ if the base line for the operator""s guess is not the bearing on which the actual evasive action is based. Moreover, in some situations, bearing from the target vehicle to the pursuing vehicle might actually dictate an entirely different evasive action from that selected by the operator on the launching vehicle even though only a small difference exists in the situation perceived by the operator in advance and at the target vehicle at alertment.
More recently, and as disclosed in our U.S. Pat. No. 6,006,145 (1999) a pursuing vehicle, such as a torpedo, is placed on an intercept trajectory from a launching vehicle to a target vehicle with evasion capabilities. Models of the pursuing vehicle and evading target provide proposed trajectories based upon various environmental considerations. A guidance system uses estimates of initial operating parameter solutions, such as gyro angle, alertment time and intercept time, to begin a convergent, iterative process that defines final operating parameter solutions from which the guidance parameters are determined and transferred to the pursuing vehicle at launch. During each iteration, the solution determines an alertment time and an alertment bearing from the target vehicle to the pursuing vehicle at the alertment time. A selected evasive strategy includes a turn that is calculated relative to the alertment bearing.
As more clearly described in the above-identified U.S. Pat. No. 6,006,145 the firing solutions assume that the target becomes alerted when a pursuing vehicle comes within a predefined alertment range. This range constrains the solution provided by that method and apparatus as a set of non-linear equations as solved for three unknowns, namely: (1) gyro turn, (2) intercept time and (3) alertment time wherein the alertment time depends upon a priori knowledge of alertment ranges.
However, there are certain tactical situations in which it is likely that the target vehicle will only become aware of a pursuing vehicle launch when it is enabled. For example, if the pursuing vehicle is a torpedo, the target vehicle may not become aware of the torpedo""s presence until the torpedo enables its active sensors. This is known as xe2x80x9cenablementxe2x80x9d. In this particular situation the solution provided by U.S. Pat. No. 6,006,145 is not valid for two reasons. First, no alertment range can be given; it is only possible to define an alertment time. However, that is the enable time. Second, the alertment range is no longer constrained within the computational loop. As many tactical situations will involve such a situation, it becomes important that any method of obtaining a firing solution take such a situation into account.
Therefore it is an object of this invention to provide a control method and apparatus for producing guidance parameters for use by a pursuing vehicle at launch that take into account diverse potential evasive maneuvers of a target vehicle.
Another object of this invention is to provide a control method and apparatus for providing guidance parameters to a pursuing vehicle for use at launch that take into account situations in which the target vehicle does not become aware of the pursuing vehicle until enablement.
Yet another object of this invention is to provide a control method and apparatus for providing guidance parameters to a pursuing vehicle for use at launch a short interval after a launching vehicle obtains an estimate of target vehicle state for producing an intercepting trajectory to a target that is not alerted to the presence of the pursuing vehicle until enablement and thereafter takes evasive action.
In accordance with one aspect of this invention, a control method for directing a pursuing vehicle from a launching vehicle to a target vehicle by supplying, to guidance means in the pursuing vehicle, operating parameters prior to the launch. The pursuing vehicle includes means that are enabled after launch; and the target vehicle becomes alerted to the presence of the pursuing vehicle upon the enablement of those means. The control method includes the steps of generating a representation of a characteristic trajectory from a generic model of pursuing vehicle trajectory, generating, in response to data from the identification means, a representation of a characteristic trajectory from a generic model of target vehicle trajectory including the expected enablement range and a plurality of possible evasive actions for the target vehicle, providing initial values for operating parameters. Then the method iteratively propagates the characteristic trajectories to intercept in response to the initial values of the operating parameters according to a plurality of approximation relationships until the solutions converge. The method also includes the steps of selecting a target vehicle evasive maneuver, and transferring the operating parameters that produce the convergence to the pursuing vehicle guidance means.
In accordance with another aspect of this invention a control system directs a pursuing vehicle from a launching vehicle to a target vehicle by supplying, to guidance means in the pursuing vehicle, guidance parameters prior to launching wherein the launching vehicle includes identification means for establishing predetermined target vehicle operating characteristics. The pursuing vehicle includes sensors that are activated at the run-to-enable time. The target vehicle becomes alerted to the pursuing vehicle when the sensors are enabled. The control system generates a representation of a characteristic trajectory from a generic model of pursuing vehicle trajectory and, in response to data from the identification means, a representation of a characteristic trajectory from a generic model of target vehicle trajectory including a plurality of evasive maneuvers. Initial values for the operating parameters are provided to the control system. The control system then iteratively propagates the characteristic trajectories in response to the initial operating parameters according to a plurality of approximation relationships until the solutions converge. An alertment range from the target vehicle to the pursuing vehicle at the run-to-enable time is calculated. The control system also determines course changes as a result of an evasive maneuver by the target submarine. The operating parameters that produce the convergence are transferred to the pursuing vehicle guidance means.